Changes in Anthocyanins during Food Processing: Influence on Color

Chapter 4

Changes in Anthocyanins during Food Processing: Influence on Color Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 19, 2015 | http://pubs.acs.org Publication Date: January 4, 2001 | doi: 10.1021/bk-2001-0775.ch004

Cristina García-Viguera and Pilar Zafrilla Lab. Fitoquímica, Dept. Ciencia y Tecnología de los Alimentos, C E B A S - C S 1 C , Murcia, Spain (phone: +34-968-215717, fax: +34-968-266613; email: [email protected])

The influence o f different factors has been studied in order to determine their effects on anthocyanin concentration and color in several products, i.e., raspberry and strawberry jam and pomegranate juice and jelly. The factors investigated here were fruit variety, freezing prior to processing and storage, the use of additives (ascorbic acid or benzoate) and pH. Results showed that freezing the fruit prior to jam manufacture, or addition of benzoate did not produce significant differences in concentrations of anthocyanins or color changes. However, other factors, such as variety or addition of ascorbic acid, did give products with differences in anthocyanins and/or color. Nevertheless, these differences in anthocyanin concentrations were not directly related to color changes. p H variations must also be considered i f a more red hue is required. However, one of the main factors that has to be considered is the processing and storage time and temperature. Long storage periods at temperatures over 25°C or processing at boiling temperature for long times cause anthocyanin degradation resulting in unacceptable colors. Furthermore, the relationship between anthocyanin degradation and loss o f red hue is more pronounced when juices are analyzed than when jams are studied.

One of the main problems that the food industry encounters is the stability of color in red fruit products. Loss of red color and increased browning during production and storage of raspberry or strawberry products are influenced by many factors. These include temperature and time o f processing (7,2) and storage (3,4\ pH, acidity, phenolic compounds, sugar, fruit maturity, thawing time (e.g., 5-S), and fruit cultivar (9). 56

© 2001 American Chemical Society In Chemistry and Physiology of Selected Food Colorants; Ames, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2001.

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Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on February 19, 2015 | http://pubs.acs.org Publication Date: January 4, 2001 | doi: 10.1021/bk-2001-0775.ch004

One of the objectives of our research is to determine the influence of some of these parameters on strawberry or raspberry jams, as well as on novel pomegranate-derived products, such as juices, jams and jellies. Here we shall summarize some of the results obtained with these manufactured products. Specifically, we shall focus on the influence of variety, processing and storage time and temperature on raspberry and strawberry jams (10-12) and also the effect of pH, addition of ascorbic acid and benzoate on some pomegranate products (13-16).

Materials and Methods Raspberry and strawberry fruit were harvested, stored and jam was prepared as previously reported (10-12). Pomegranates were harvested in September 1996 and juices and jellies were manufactured as previously described (13,15). Anthocyanin extraction, H P L C analyses, identification and quantification have also been described (10-13,15). CIEL*a*b* color measurements of jams and jellies were performed by reflectance on a color spectrophotometer model CM-508Î (Osaka, Japan) with a granular cover set C M - A 4 0 (77). Juices were measured in glass cells of 2 cm path length (CT-A22), using the same apparatus coupled with transmittance adaptator model CM-A760 (15). Color differences were expressed as A E * = [(AL*) + (Aa*) + (Ab*) ] . A E * 15

Figure 4. Percentage of strawberry anthocyanin loss during jam preparation under different conditions (Ind= Industry conditions, LabI0=jams prepared in the laboratory, 10 min. boiling, Labi5= 15 min. boiling and Lab>15= boiled over 15 minutes). Fruit anthocyanin concentration (white bars), Jam anthocyanin concentration (black bars)

When the boiling time was reduced to 10 min in the laboratory, the degradation was reduced to ca. 16%, and when it was longer that 15 min the degradation increased drastically to ca. 80%, rendering a product with an unacceptable appearance. These differences in anthocyanin concentrations were also detected when color analyses were done. Jams prepared under industrial conditions or in the laboratory, by boiling for 10 minutes, possessed similar color (ΔΕ*= 5.27). Any variance was due to a higher CIEL* value for jams manufactured using the industrial process, rendering a lighter product, but with the same red hue. Moreover, for those jams prepared using traditional conditions in the laboratory (15 min boiling), the color became more purple (AE*=15.17), due to lower CIEa* and CIEb* values. Again, those that were boiled for longer than 15 min (ca. 80% anthocyanin loss), possessed an unacceptable brownish color, very different from those manufactured under industrial conditions (AE*= 23.75). Consequently, we can deduce that there is a relationship between anthocyanin concentration and color, since when the free anthocyanin loss is very high the color is unacceptable. Due to this, processing factors (time and temperature) should be

In Chemistry and Physiology of Selected Food Colorants; Ames, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2001.

61 considered when producing this foodstuff, in order to minimize anthocyanin degradation.


Influence of Storage Conditions The previous sections have discussed the influence of certain parameters that affect the color of processed products, such as jams, and the relationship between the anthocyanin concentration and degradation. In this section, discussion focuses on one of the most decisive factors that modify pigment concentration and its relationship with color, i.e., storage. Previous studies with raspberry jams (10) have demonstrated that storage temperature has a decisive effect on color when these products are kept at 30°C for 6 months, independent of the variety or i f the fruit was previously frozen or not. The resulting products have a brown hue, with no detectable free anthocyanins. Similar results were obtained when strawberry jams were analyzed (//) indicating that when the product was stored at 37°C, anthocyanin degradation was more than 98% after 3 months (Figure 5), while the same level of degradation occurred after 6 months storage at 20°C for all three varieties used (Chandler, Tudla and Oso Grande). When comparing, for example, the color of jams prepared from Oso Grande, it was seen that, even i f no anthocyanins were detectable at either temperature, those stored at 37°C possessed a more brownish hue. This was due to changes in the CIEL*a*b* parameters during storage at 37°C (ΔΕ*= 20.04, when comparing initial jams with those stored for a few months at 37°C), but a smaller color loss occurred i f stored for the same time at 20°C, rendering, in this latter case, jams with minor color alterations (ΔΕ*= 10.17), even i f loss of anthocyanins was more than 98%. Moreover, when the storage temperature was decreased to 5°C (12) the percentage loss of anthocyanins fell to 80% (Figure 5), and an increase in the red hue was observed when compared to the initial value (AE*=8.56). Also, differences in color where detectable after 6 months between those jams stored at 5°C and 20°C (AE*=10.17). Also, the influence of light during storage has been studied, in relation to anthocyanin content and color stability of strawberry jam (12). The obtained results showed that no significant differences were detected between those jams stored under periodical daylight conditions and those stored in the dark for 6 months. The above mentioned results are in accordance with general findings that anthocyanin concentrations decrease during storage and that anthocyanins are markedly influenced by temperature and storage time (5,18). However, the rate of color loss is slower than the rate of anthocyanin degradation. Therefore, other factors, discussed elsewhere (10,17), may play a significant role in the expression of colour by co-pigmentation, polymerization or some other physicochemical processes. In the same way, the variety of fruit, or method of preparing the jam with fruit frozen for a short time, can influence color or anthocyanin concentration after storage at an elevated temperature (37°C) for 6 months (10,11).



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Time (days)

Figure 5. Percentage of anthocyanin and color degradation in strawberry jams, after storage at 5°C (Φ), 20°C (Εφ and 37°C (A). Black symbols= Anthocyanin; white symbols = CIEa* value

Influence of Other Factors Other factors that could affect certain manufactured products, specifically the addition of ascorbic acid or benzoate and changes in pH, have been studied in relation to novel pomegranate products (juices and jellies). Benzoate is an additive used by the industry for its antimicrobial properties When the influence of this additive (0.1% w/v) in a pomegranate juice was studied (16), the results showed that it had no influence on anthocyanin degradation, i.e., after 48 days at 25°C, the percentage loss of these pigments in juices with or without benzoate was the same (ca. 93%) and also the color was very similar at the end of the storage period (ΔΕ*=3.03, Figure 6). Nevertheless, significant color differences were found between the fresh juices and those stored under the above conditions (AE*ca. 55.15, Figure 6), mainly because of a great loss in the red hue related to CIEa* value (ca. 82% loss).



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Figure 6. CIEL*a*b* values obtained for pomegranate juice at day 0 (white bars), after storage at 25°C for 48 days control (grey bars) and with benzoate addition (black bars). Ascorbic acid ( A A ) is commonly added to fruit juices to prevent browning as well as an additional source of vitamin C. Nevertheless, the effect of this compound on anthocyanin degradation and its consequent effect on color has been studied previously (19). We also analyzed the effect of ascorbic acid in relation to anthocyanin and color variations in pomegranate juice (15,16). Results showed that the addition of ascorbic acid increased the rate of anthocyanin degradation, stored at 5°C for 160 days (80% and 63% loss with and without ascorbic acid, respectively), besides differences in colors (ΔΕ*=13.04) mainly due to lower CIEa* and CIEb* values and a higher CIEL* value for those prepared with ascorbic acid (Figure 7).

Figure 7. CIEL*a*b* values obtained for pomegranate juices, with ascorbic acid (black bars) and without ascorbic acid addition (white bars).



64 Finally, the consequence of modifying the p H on a novel pomegranate jelly product was determined (13,14). Results demonstrated that acidification of pomegranate juice, cultivar Mollar, with an initial p H of 4, (to pH 3 and pH 3.5), prior to jelly preparation, does affect the final anthocyanin concentration and has a perceptible influence on color. Thus, the anthocyanin concentration was 18% higher when jellies were prepared with juice acidified to p H 3.5 and 43% higher when prepared with pH 3 juice. This was confirmed by color analysis since a brown hue was detected for those products prepared with non-acidified juices (pH 4), while those prepared with p H 3 juice presented a marked red hue (ΔΕ*=10.67). Smaller differences where seen for those prepared with p H 3.5 juice (ΔΕ*=6.70). This was due to a change in the CIEa* value which was much higher for products prepared from juice of lower pH (Figure 8).

Figure 8. CIEL*a*b* values obtained for jellies prepared with pomegranate juice of pH 4 (white bars), pH 3.5 (grey bars) and pH 3 (black bars).

Conclusion We can conclude that anthocyanin concentrations decrease during storage and that anthocyanins and color are markedly influenced by temperature and storage time. However, the rate of color loss is slower than the rate of anthocyanin degradation. In the same way, the variety of fruit, method of preparing the jam and freezing the fruit for long periods (over 6 months) have significant effects on colour or anthocyanin concentration. In contrast, using short period frozen fruit (24 hours) has no significant influence on these parameters after stored at high temperature (37°C) for 6 months. Addition of benzoate has no influence on anthocyanin or color degradation, although p H and ascorbic acid do affect these parameters.


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Literature Cited 1. Markakis, P. Anthocyanins as Food Colours; Markakis, P. Ed, Academic Press: New York, 1982, pp 163-180. 2. Pilano, L.S.; Wrolstad, R.E.; Heatherbell, D.A. J. Food Sci. 1985, 50, 1121-1125. 3. Adams, J.B.; Ongley, M . J . J. Food Technol. 1973, 8, 139-145. 4. Irzyniec, Z.; Klimezak, J.; Michalowski, S. Bioavailability '93- Nutritional, Chemical & Food Processing Implications of Nutrient Availability. Part III, 1993, pp 398-403. 5. Withy, L.M.; Nguyen, T.T.; Wrolstad, R.E.; Heatherbell, D.A. J. Food Sci. 1993, 58, 190-192. 6. Wrolstad, R.E.; Putman, T.P.; Varseveld, G.W. J. Food Sci. 1970, 35, 448-452. 7. Abers, J.E.; Wrolstad, R.E. J. Food Sci. 1979, 44, 75-78. 8. Rommel, Α.; Heatherbell, D.A.; Wrolstad, R.E. J. Food Sci. 1990, 55, 1011-1017. 9. Bakker, J.; Bridle, P.; Bellworthy, S.J. J. Sci. Food Agric. 1994, 64, 31-37. 10. Garcia-Viguera, C.; Zafrilla, P.; Artés, F.; Romero, F.; Abellán, P.; TomásBarberán, F.A. J. Sci Food Agric. 1998, 78, 565-573. 11. Garcia-Viguera, C.; Zafrilla, P.; Romero, F.; Abellán, P.; Artés, F.; TomásBarberán, F.A. J. Food Sci. 1999, 64, 243-247. 12. García-Viguera, C.; Zafrilla, P.; Tomás-Barberán, F . A . J. Food Sci. Technol. 1999, 5:6, (in press). 13. Maestre, J.; Senabre, R.; Melgarejo, P.; García-Viguera, C. I International Symposium on Pomegranate; Melgarejo, P.; Martínez, J.J.; Martínez, J. Eds; Universidad Miguel Hernández: Orihuela (Alicante, Spain), 1998, 1/7-7/7. 14. Senabre, R.; M s Thesis; Universidad Miguel Hernández, Orihuela, (Alicante, Spain) 1998. 15. García-Viguera, C.; Marti, N.; Bridle, P.; Pigments in Food Technology; Mínguez, M.I. ; Jarén, M.; Hornero, D . Eds.; CSIC; Sevilla, Spain, 1999; 307-310. 16. Martí, N.; Ms Thesis; Universidad Miguel Hernández, Orihuela (Alicante, Spain), 1998. 17. Zafrilla, P.; Valero, Α.; García-Viguera, C.; Food Sci. Technol. Inter. 1998, 4, 99105. 18. Jackman, R.L.; Smith, J.L. Natural Food Colorants; Hendry, G.A.F., Houghton, J.D. Eds. Blakie Academic &Professional: Glasgow (U.K.), 1996, pp 449-309. 19. García-Viguera, C.; Bridle, P.; Food Chem. 1998, 64, 21-26.


Changes in Anthocyanins during Food Processing: Influence on Color

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